Bumper and Limit switches

i got bored and opened up a vex limit switch to see how it worked(vex uses PWM, and i was curious). i was surprised to find that the red wire was NOT connected to any of the switch terminals. only the black and the white wires were attatched, and the switch works! well, black and red are the power, and only black was connected, and the white wire is the signal for the current…so, how does this work? i opened up another limit switch and a bumper switch, same thing. there isn’t even a sign of someone having tried to solder on the red wire. and why would vex put in a wire that they don’t need? that’s a waste of money!


a switch works like this, the pin its plugged into will stay high (5V, ‘1’), if you press the switch the connection will be completed between ground and the i/o pin

this makes the i/o pin go low (0V, ‘0’)

the reason for the red wire is just for stability of the connection

oh and im not quite sure (i honest to god forget) but i think there’s something 'bout it in the inventors guide (i tihnk, i havent touched that guide for a long time)

what do you mean by ‘stability of the connection’?

well take out a tower from underneath a bridge and it suddenly becomes less stable

taking out the red pin would allow more freedom which means the wire could fall out in use

oh i see what you mean, but why can’t there just be a stub instead of a whole wire to secure to connection?

There are a few other reasons I can think of…

I am sure that IFI (AKA VexLabs) buys 10’s of 1000’s of feet of that WHITE-RED-BLACK three conductor wire, since more quantity, costs less per Unit (usually in Cents per Foot).

Since the RED is the middle wire…

  1. IFI would have to stock some WHITE-BLACK two conductor wire, just for Switches (expensive in that two different types of wire spools would need to be stocked [MANAGEMENT] and possibly a loss of a discount because of a smaller quantity of a given type of wire).

  2. Someone would have to strip the RED out of the middle on the WHITE-RED-BLACK, leaving two individual wires that would be “glued” back together and made into the Switches (VERY expensive for the Labor and kind of a silly use of time, not to mention very boring work).

The bottom line is that giving you the extra, not needed wire, is the most economical way of making the Switches.

and it would look this cool as just a stub :cool::D:rolleyes:

you would have to specially order them or make them yourself because im not sure anyone manufactures that type

you could also make your own switches easily by buying a PWM cable, switch of any type and some cheap soldering skills (although most roboteers already have that :D)